Convex aspherical mirrors are widely used in reflective optical systems, but high-precision shape measurement technology is always a difficult problem in optical manufacturing. In order to achieve high- precision detection of convex aspheric with small aperture and large asphericity, a null test interference detection technique based on computer generated hologram (CGH) was proposed. Firstly, the detection principle and method of this technology were described in detail, and the key technical points in the processing of testing CGH and alignment CGH design were given. Then, combined with engineering application, the corresponding CGH was designed and manufactured for convex aspheric with the aperture of 15 mm, the vertex curvature radius of 11.721 mm and its asphericity of 72 μm, and the null test interference detection experiments based on CGH were completed. Finally, the accuracy of the proposed method was verified by cross-comparison with Luphoscan detection technique. This technology provides an effective method for high-precision testing of small aperture convex aspheric and has significant engineering application value.